The manufacture of electronic circuit components and the packaging of those components customarily involves the deposition of one or more layers of material upon a base element or substrate. During the manufacturing process it is occasionally necessary to subject the component to a cleansing purge to remove unwanted contaminants that may have formed in a previous process step and to prepare the part for the formation of additional material on one or more selected sites. For example, to maximize the metallurgical affinity of solder (diagrammatically shown at 11 in FIG. 1) to an electrode terminal 13, the terminal metal should be free of surface contaminant material (e.g. oxide and organics) 15, before application of the solder. Similarly, with reference to the diagrammatic illustration of an electronic circuit package 20 in FIG. 2, prior to depositing a layer of `branding code` ink 21 to the surface 23 of a metallic (e.g. nickel) branding lid 25, it is necessary to clean the surface of the metallic branding lid 25, in order ensure that the ink will strongly adhere to the lid and tolerate various solvents that are used to clean the part before and after it is eventually soldered in place on an electrical circuit board.
Conventional branding techniques on nickel-plated circuit packaging lids involve the use of a number of ink supplier-recommended wet chemical etching solutions, such as Markum 535, Markum 310, IPA, which have been accepted by the industry as being effective in removing oxide and organic contaminants, thereby sufficiently increasing the surface energy of the lid to the adherence of the ink to meet MIL-STD testing compliance for brand permanency. In effect, the chemical solution physically etches away the surface of the lid and thereby removes surface oxide and organics down to some level of `clean` metal, in order that the number of uncontaminated nickel bonding sites will be increased.
Unfortunately, chemical etching solutions have a significant drawback, - the entire circuit package is immersed in the etching solution in order to clean or etch the oxide contaminants off the lid. As a consequence, the solution not only cleans the lid, but, because of its substantial caustic properties (Markum 535, for example, contains monoethanolamine which has a pH greater than ten), it etches or physically attacks other portions of the package, such as the soldered leads, the lid-to-seal ring weld area, and various plated metallic markings or codes on the package, as well as the ceramic package itself. It has been found that this ancillary etch not only degrades the cosmetic appearance of the part, but may detrimentally affect its overall reliability. Moreover, upon completion of the chemical etch, because the package is subjected to an oven drying step at an elevated temperature, following a rinse, oxide again begins to immediately form on the `cleaned` surface of the nickel. As a result, when the part emerges from the drying oven, time is of the essence for successfully depositing the branding ink, which must ordinarily conducted within minutes of the oven drying step.